Method for operating a power plant and power plant

ABSTRACT

A method for operating a power plant is disclosed. The power plant comprises a power machine and a flue gas flow path following downstream of the power machine. A flue gas flow path is scavenged with fresh air before the flue gas flow path is acted upon with flue gas. To carry out the scavenging operation, air is extracted from a pressure accumulator and the air is introduced into the flue gas flow path downstream of the power machine. The power machine can be an exhaust gas heat exchanger.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 U.S.C. §119 toGerman Application No. 10 2004 028 531.4, filed Jun. 11, 2004 and is acontinuation application under 35 U.S.C. §120 of InternationalApplication No. PCT/EP2005/052595, filed Jun. 7, 2005 designating theU.S., the entire contents of both of which are hereby incorporated byreference.

FIELD

A method for operating a power plant is disclosed, including a powerplant for carrying out the method.

BACKGROUND INFORMATION

It is known to scavenge the exhaust gas tract of gas turbines or gasturbo groups with fresh air after a standstill before the flue gasestake action. This avoids the situation where combustible gases, whichmay potentially accumulate during lengthy standstill phases, ignite whenthe plant is put into operation. The importance of this scavengingoperation comes to the fore particularly when the arrangement of exhaustgas heat exchangers in the flue gas tract of a gas turbo group or ofanother thermal power engine provides large volumes in which ignitablegas mixtures may potentially accumulate. For example, in combined-cyclepower plants, to drive the gas turbo group for several minutes withoutfiring before the gas turbo group is put into operation, in orderthereby to generate a flow of fresh air through the waste-heat recoverysteam generator. Only when the volume of the waste-heat recovery steamgenerator has been conveyed, for example, five times by the gas turbogroup does an ignition of the gas turbo group take place. On account ofthe limited maximum throughput through the gas turbo group, such anoperation takes up several minutes, typically of the order of tenminutes to 20 minutes. The result of this is that power plants of thistype can deliver power to the network, from standstill, only after acomparatively long delay time. In air accumulator plants, too, thestored fluid is in most instances heated in an exhaust gas heatexchanger before it is supplied to the expansion machine. Accordingly,even these plants, which are intended per se for covering peak load andin which short start-up times are therefore desirable, can deliver tothe network only after delay.

SUMMARY

Applicant has disclosed a method for operating a power plant which canremedy these problems. An exemplary method as disclosed can avoid theseand other disadvantages of the prior art. In one aspect, the disclosedexemplary method can be employed to drastically reduce the waiting timesfor putting a power plant into operation which are caused by thescavenging operation.

One aspect of the disclosed method, therefore, is not to convey the airrequired for carrying out the scavenging operation by means of the powerengine preceding the flue gas flow path or to supply this air to theflue gas flow path through the power engine, but, instead, to extractthe air required for carrying out the scavenging operation, underpressure, from an accumulator volume and to supply it to the flue gasflow path essentially directly, that is to say bypassing preceding powerengines. The disclosed method is suitable most especially for thescavenging of exhaust gas heat exchangers, in particular of waste-heatrecovery steam generators, which are arranged in the flue gas flow pathand which serve, for example, for the generation of fresh steam for thesteam circuit of a combined-cycle plant or for the generation of processsteam or heating steam, or of air preheaters, such as serve, for examplefor supplying heat to the accumulator fluid of air accumulator plants.

The disclosed method is suitable particularly for use in air accumulatorplants having an accumulator volume which is filled with compressed air.The air which is required for scavenging the flue gas flow path can inthis case be extracted directly from the accumulator volume of thepressure accumulator plant. If, in a simple gas turbine plant or acombined-cycle plant, such an accumulator volume is absent, anaccumulator vessel may advantageously be arranged above ground or belowground, which is connected to a charging compressor. The accumulatorvolume is then advantageously designed such that its standard volume,that is to say its accumulator capacity with respect to the ambientpressure, amounts to 5 to 30 times the volume to be scavenged. A pistoncompressor or screw compressor may then be used, for example, as acharging compressor and can charge this accumulator volume to thenominal pressure within a time span of, for example, one hour.

In one exemplary embodiment of the method, the air is introduced intothe flue gas flow path directly upstream of an exhaust gas heatexchanger. In another exemplary embodiment of the method, in a powerplant in which a firing device is arranged downstream of the powerengine and upstream of an exhaust gas heat exchanger, the air isintroduced upstream of the firing device into the flow path leading fromthe power engine to the firing device.

In a further exemplary embodiment of the method, during the scavengingoperation, the power engine is set in movement, that is to say, forexample, a turbine is rotated. As a result, in addition to the first airmass flow which is extracted from the pressure accumulator and isintroduced into the flow path downstream of the power engine, a secondair mass flow is conveyed through the flue gas flow path. For example,when the power engine and the accumulator fluid expansion machine areidentical, that is to say when, in stationary operation, the accumulatorfluid mass flow expanded in the expansion machine is supplied to anexhaust gas heat exchanger on the primary side, a second air mass flowis conducted out of the accumulator volume into the expansion machineduring the method.

An exemplary power plant suitable for carrying out the disclosedexemplary methods comprises a line with a shut-off member, said lineleading from the pressure accumulator to the flue gas flow path and, inparticular, to the primary-side flow path of an exhaust gas heatexchanger. In the framework of the statements made here, moreover, thatpart of a heat exchanger through which the heat-emitting fluid flows isdesignated as the primary side. Correspondingly, that part through whichthe heat-absorbing fluid flows is designated as the secondary side. Inone embodiment of this power plant, a flow path leads from the pressureaccumulator through a secondary-side flow path of the exhaust gas heatexchanger and from there to an accumulator fluid expansion machine. Inthis exemplary embodiment, the first air mass flow which is extractedfor scavenging the exhaust gas heat exchanger can be branched offupstream of the secondary-side flow path of the exhaust gas heatexchanger.

In one exemplary embodiment of the power plant, the output from theaccumulator fluid expansion machine leads to the primary side of theexhaust gas heat exchanger. Accordingly, the accumulator fluid expansionmachine and the power machine, which is arranged upstream of the exhaustgas heat exchanger, may be identical. Such a pressure accumulator plantis known, for example, from DE 102 58 594, which publication in thisrespect is incorporated by reference in the present disclosure,constituting an integral part of the present disclosure. It is alsoknown, further, from this publication to arrange a firing device in theflow path of the accumulator fluid. From DE 44 10 440, it is known,moreover, to arrange an exhaust gas heat exchanger in the exhaust gasflow of a gas turbo group and to conduct the accumulator fluid of apressure accumulator plant through this exhaust gas heat exchanger,where the accumulator fluid is heated by means of the exhaust-gas heatof the gas turbo group. Applicant's disclosure can also be employedeffectively in this case.

BRIEF DESCRIPTION OF THE DRAWING

The invention is explained in more detail below by means of exemplaryembodiments illustrated in the drawing in which, in particular:

FIG. 1 shows a first example of a power plant suitable for carrying outthe method according to the invention;

FIG. 2 shows a second example of a power plant suitable for carrying outthe method according to the invention;

FIG. 3 shows a further example of a power plant suitable forimplementing the method according to the invention; and

FIG. 4 shows a fourth example of a power plant suitable for implementingthe method according to the invention.

The exemplary embodiments and the figures should be understood as beingexplanatory and should not be used to restrict the disclosed subjectmatter.

DETAILED DESCRIPTION

FIG. 1 shows an exemplary power plant. An exemplary gas turbo group 1comprises a compressor 101, a combustion chamber 102 and a turbine 103.The type of construction of the gas turbo group is in this case notessential to the invention; it will be possible, for example, readily tomake use of a multi-shaft arrangement of a gas turbo group or else a gasturbine with sequential combustion, as is known from EP 620 362. The gasturbo group drives a generator 104 for generating useful electricalpower. In the flue gas flow path of the expanded flue gases flowing outof the turbine 103, an exhaust gas heat exchanger 202 is arranged. Thehot flue gases flow through the latter on its primary side. On thesecondary side, a fluid stored under pressure in an accumulator volume201 can be conducted through the heat exchanger 202. The mass flow ofthe accumulator fluid is controlled by the accumulator fluid actuatingmember 7. The accumulator fluid flows through the exhaust gas heatexchanger in countercurrent to the flue gas and in this case absorbsheat from the flue gases. The heated accumulator fluid is expanded inthe accumulator fluid expansion turbine 203 so as to perform work. Theturbine 203 drives the generator 204 which likewise generates a usefulelectrical power. The accumulator volume 201, the exhaust gas heatexchanger 202, the turbine 203 and the generator 204 together form apressure accumulator plant 2. It is basically possible, and is alsoknown from the prior art, to arrange the gas turbo group 1 and theaccumulator fluid expansion turbine 203 on a common shafting, the gasturbo group 1 and the accumulator fluid expansion machine 203 acting ona common generator. In times of low electricity demand andcorrespondingly low power prices, the compressor arrangement 3 isoperated in order to fill the accumulator volume 201 with compressed airwhich, in times of high electricity demand and correspondingly highpower prices, is available again for electricity generation by means ofthe turbine 203 and the generator 204. The compressor arrangement 3comprises a first compressor 301, a first cooler 302, a secondcompressor 303 and a second cooler 304 and, furthermore, a nonreturnmember 306 and a motor 305. The compressors 301 and 303 are arrangedtogether with the motor 305 on a common shaft. When the compressorarrangement 3 is in operation, air is sucked in by the compressor 301and compressed, cooled in the first cooler 302, compressed further inthe second compressor 303, cooled once again in the second cooler 304and conveyed to the accumulator volume 201 via the nonreturn member 306.The nonreturn member 306 prevents the backflow of fluid from theaccumulator volume 201 in the compressor train. After a plantstandstill, the primary side of the exhaust gas heat exchanger 202 hasto be scavenged before the gas turbo group 1 is put into operation. Thisavoids the situation where combustible gases, which have potentiallycollected on the primary side of the exhaust gas heat exchanger, ignitewhen the combustion chamber 102 is ignited. For this purpose, accordingto the prior art, the gas turbo group 1 is driven by the motivelyoperated generator 104, with the result that a flow through the primaryside of the exhaust gas heat exchanger is induced. The fresh air massflow available in this case is limited. The scavenging of the exhaustgas heat exchanger therefore takes up several minutes. In this case, thepower plant illustrated can deliver power to the network only with along delay. In the power plant illustrated in FIG. 1, therefore, a line8 branches off from the flow path of the accumulator fluid and issues,upstream of the exhaust gas heat exchanger, in the flue gas flow path ofthe gas turbo group 1. A firing device may also be arranged between theturbine 103 of the gas turbo group 1 and the exhaust gas heat exchanger202; the scavenging air line 8 can then issue, upstream or downstream ofthe firing device, in the flue gas flow path. The line may be closed oropened by means of a shut-off and/or actuating member 9. According tothe invention, when the plant is started up, the shut-off member 9 isopened. At the same time, the gas turbo group 1 can be driven by theelectromotively operated generator 104. In addition to the mass flowconveyed by the gas turbo group, accumulator fluid then flows out of theaccumulator volume 201 through the exhaust gas heat exchanger 202. Thefresh air mass flow then available for scavenging the exhaust gas heatexchanger amounts to a multiple of that which is provided by the gasturbo group driven empty. For this reason, the time necessary forscavenging the primary side of the exhaust gas heat exchanger isappreciably reduced, and the power plant can deliver power to theelectricity network more quickly. After the scavenging of the primaryside of the exhaust gas heat exchanger 202, the shut-off member 9 isclosed again. The further start-up operation of the power plant is thencarried out in a way known to a person skilled in the art.

In the exemplary power plant illustrated in FIG. 2, the gas turbo groupis omitted. Compressed air stored in the accumulator volume 201 flowsvia the actuating member 7 into the secondary-side flow path of the heatexchanger 202. The accumulator fluid is heated there in heat exchangewith a flue gas flowing on the primary side of the heat exchanger. Theheated accumulator fluid flows to the accumulator fluid expansionturbine 203 where the accumulator fluid is expanded so as to performwork. The shaft power generated in this case serves for driving thegenerator 204. The expanded accumulator fluid flows into a firing device205 and is heated there. The hot flue gas occurring flows into theprimary side of the exhaust gas heat exchanger 202 and, when it flowsthrough, is cooled in heat exchange with the accumulator fluid, beforeit flows out into the surroundings through a chimney 4. In the powerplant illustrated in the exemplary embodiment, when the power plant isput into operation again after a standstill the actuating member 7 canbe opened a specific amount for the necessary scavenging of the primaryside of the exhaust gas heat exchanger 202, with the result thataccumulator fluid flows through the turbine 203, the firing device 205and the primary side of the exhaust gas heat exchanger 202 and thusensures that combustible gases are no longer contained there. At thesame time, the shut-off member 9 is opened, with the result thatadditional accumulator fluid is conducted via the line 8 into the flowpath downstream of the turbine 203. This accumulator fluid can beintroduced upstream of the firing device, but, as illustrated by thedashed line, can also be introduced into the flue gas flow path directlyupstream of the primary side of the exhaust gas heat exchanger 202.Introducing the scavenging air upstream of the firing device 205 has theadvantage in this case that, by means of the air introduced there, thefiring device can be put into operation at a very early stage in thestart-up operation and the exhaust gas heat exchanger 202 can bepreheated, with the result that the start-up times can be furtherreduced.

The exemplary embodiment illustrated in FIG. 3 corresponds, in terms ofcarrying out the scavenging operation for the primary side of theexhaust gas heat exchanger 202, essentially to what has already beendiscussed in connection with FIG. 2. However, the power plantillustrated here differs in terms of the accumulator fluid expansionmachine. This corresponds essentially to a type of construction alsoknown from DE 102 58 594. Accumulator fluid flows through the exhaustgas heat exchanger 202 on the secondary side before it is partlyexpanded in a first turbine 206. The partly expanded accumulator fluidflows to a combustion chamber 207 where it is heated as a result of thecombustion of a fuel. The flue gas occurring is expanded further in theturbine 203 and flows through the exhaust gas heat exchanger 202 on theprimary side, in countercurrent to the accumulator fluid, the flue gasbeing cooled in heat exchange with the accumulator fluid flowing on thesecondary side. Of course, as proposed in DE 102 58 594, a furtherfiring device may be arranged between the turbine 203 and theprimary-side flow path of the exhaust gas heat exchanger 202. The issueof the scavenging fluid which is routed via the line 8 and the shut-offmember 9 may then likewise take place upstream or downstream of thefiring device.

FIG. 4 exemplifies an application of the disclosed method with referenceto a combined-cycle plant. The combined-cycle plant comprises the gasturbo group 1 and the water/steam circuit 4. The water/steam circuitcomprises a waste-heat recovery steam generator 402 through which theflue gas from the gas turbo group 1 flows on the primary side. A boilerfeed pump 409 conveys a feed water mass flow through the secondary-sideflow paths of the waste-heat recovery steam generator 402. Fresh steamis generated from the feed water by means of the exhaust gas heat of thegas turbo group and is supplied to a steam turbine 403 via a fresh steamactuating member 407. In the steam turbine 403, the steam is expanded soas to perform work, and a generator 404 is driven by means of the usefulpower thus generated. It is also known in the prior art for the steamturbine 403 and the gas turbo group 1 to be of single-shaft design suchthat they act on a common generator. The expanded steam is condensed ina condenser 408, and the condensate occurring is supplied to the boilerfeed pump 409 again. The water/steam circuit is in this case illustratedin greatly simplified form. Moreover, the embodiment of the water/steamcircuit is not essential to the invention. The steam could just as wellbe used for process or heating purposes. In conventional combined-cycleplants, the waste-heat recovery steam generator 402 has to be scavengedbefore the gas turbo group 1 is started, wherein the gas turbo group 1is set in rotation and therefore a flow through the waste-heat recoverysteam generator is induced. As illustrated initially, this operationtakes up several minutes. In the power plant illustrated, an airaccumulator 201 is arranged, which is filled with compressed air by acompressor arrangement 3. Accordingly, for scavenging the primary-sideflow path of the waste-heat recovery steam generator 402, the shut-offmember 9 is opened and air is introduced from the accumulator 201through the line 8 into the flue gas flow path of the gas turbo group.The scavenging air mass flow achievable here is substantially greaterthan the air mass flow which can be achieved when the gas turbo group isrotated at a limited rotational speed. The scavenging operation isthereby terminated substantially more quickly. That is to say, thecombustion chamber 102 of the gas turbo group can be ignited earlier,with the result that the combined-cycle plant can be connected to thenetwork more quickly. As compared with the exemplary embodimentsillustrated in the above figures, the accumulator volume 201 issubstantially smaller because the stored air does not serve for powergeneration, but for scavenging the exhaust gas tract in the gas turbogroup 1. It may be assumed, as a rule of thumb, that, for scavenging thewaste-heat recovery steam generator 402, the volume of the latter shouldbe replaced about five times. The result of this is that the air massstored in the accumulator volume 201 should be greater than five timesthe content of the steam generator 402. Values of between five times andthirty times can be selected. This makes it possible, after a possiblyfaulty starting attempt, to scavenge the waste-heat recovery steamgenerator 402 a second time with air stored in the accumulator volume201. The charging compressors 3 may also be configured correspondinglyfor relatively low mass flows. For example, piston compressors or screwcompressors may be employed here.

Exemplary embodiments described above and the drawing also open up to aperson skilled in the art embodiments of the invention which differ fromthe exemplary embodiments and which are contained in the scope of thepatent claims. The invention, as characterized in the claims, islikewise suitable for scavenging the exhaust gas tract of a simple gasturbo group.

It will be appreciated by those of ordinary skill in the art that theexemplary circuit breakers described here can be embodied in variousspecific forms without departing from the essential characteristicsthereof. The presently disclosed embodiments are considered in allrespects to be illustrative and not restrictive. The scope of theinvention is indicated by the appended claims, rather than the foregoingdescription, and all changes that come within the meaning and range ofequivalence thereof are intended to be embraced.

LIST OF REFERENCE SYMBOLS

-   1 Gas turbo group-   2 Pressure accumulator plant-   3 Compressor plant-   4 Chimney-   7 Accumulator fluid actuating member-   8 Scavenging air line-   9 Shut-off member-   101 Compressor-   102 Combustion chamber-   103 Turbine-   104 Generator-   201 Pressure accumulator, accumulator volume-   202 Heat exchanger, exhaust gas heat exchanger-   203 Accumulator fluid expansion machine-   204 Generator-   205 Firing device-   206 Accumulator fluid expansion machine-   207 Combustion chamber-   301 Compressor-   302 Cooler-   303 Compressor-   304 Cooler-   305 Motor-   306 Nonreturn member-   402 Exhaust gas heat exchanger, waste-heat recovery steam generator-   403 Steam turbine-   404 Generator-   407 Fresh steam actuating member-   408 Condenser-   409 Feed pump

1. A method for operating a power plant, which power plant comprises: apower machine and a flue gas flow path following downstream of the powermachine, which method comprises: scavenging the flue gas flow path withfresh air before the flue gas flow path is acted upon with flue gas,wherein, to carry out the scavenging operation, air is extracted from apressure accumulator and the air is introduced into the flue gas flowpath downstream of the power machine.
 2. The method as claimed in claim1, the heat-emitting primary side of an exhaust gas heat exchanger beingarranged in the flue gas flow path.
 3. The method as claimed in claim 2,the exhaust gas heat exchanger being a waste-heat recovery steamgenerator.
 4. The method as claimed in claim 1, the pressure accumulatorbeing a pressure accumulator of a pressure accumulator plant with anaccumulator fluid expansion machine.
 5. The method as claimed in claim4, the power machine and the accumulator fluid expansion machine beingidentical, wherein a second air mass flow is conducted out of theaccumulator volume into the expansion machine during the scavengingoperation.
 6. The method as claimed in claim 4, a secondary-side flowpath of the exhaust gas heat exchanger leading from the pressureaccumulator to the accumulator fluid expansion machine comprisingbranching off the air upstream of the secondary-side flow path of theexhaust gas heat exchanger.
 7. The method as claimed in claim 2,comprising introducing the air into the flue gas flow path directlyupstream of the exhaust gas heat exchanger.
 8. The method as claimed inclaim 2, a firing device being arranged downstream of the power machineand upstream of the exhaust gas heat exchanger, wherein the air isintroduced upstream of the firing device into the flow path leading fromthe power machine to the firing device.
 9. The method as claimed inclaim 8, wherein the power machine is set in movement during thescavenging operation.
 10. A power plant, comprising: a pressureaccumulator; at least one power machine; and a flue gas flow patharranged downstream of the power machine, wherein a line with a shut-offmember leads from the pressure accumulator to the flue gas flow path andissues into the flue gas flow path downstream of the power machine. 11.The power plant as claimed in claim 10, wherein the heat-emittingprimary-side flow path of an exhaust gas heat exchanger is arranged inthe flue gas flow path, and the line issues in the flue gas flow pathupstream of the exhaust gas heat exchanger.
 12. The power plant asclaimed in claim 11, wherein the exhaust gas heat exchanger is awaste-heat recovery steam generator.
 13. The power plant as claimed inclaim 10, comprising an accumulator fluid expansion machine and anaccumulator fluid flow path leading from the pressure accumulator to theaccumulator fluid expansion machine.
 14. The power plant as claimed inclaim 13, wherein the accumulator fluid flow path leads through aheat-absorbing secondary-side flow path of the exhaust gas heatexchanger and then to the accumulator fluid expansion machine.
 15. Thepower plant as claimed in claim 14, wherein the outflow from theaccumulator fluid expansion machine leads to the primary side of theexhaust gas heat exchanger.
 16. The power plant as claimed in claim 11,comprising a gas turbo group, the flue gas outflow of which issues inthe primary side of the exhaust gas heat exchanger.
 17. The power plantas claimed in claim 11, wherein a firing device is arranged upstream ofthe primary side of the exhaust gas heat exchanger.
 18. The method asclaimed in claim 2, the pressure accumulator being a pressureaccumulator of a pressure accumulator plant with an accumulator fluidexpansion machine.
 19. The method as claimed in claim 3, the pressureaccumulator being a pressure accumulator of a pressure accumulator plantwith an accumulator fluid expansion machine.
 20. The method as claimedin claim 5, a secondary-side flow path of the exhaust gas heat exchangerleading from the pressure accumulator to the accumulator fluid expansionmachine comprising branching off the air upstream of the secondary-sideflow path of the exhaust gas heat exchanger.